Method and apparatus for detecting coherent elastic wave energy

ABSTRACT

In the mapping of elastic wave fields in fluids, such as might be involved in recording a sonic hologram in a liquid medium overlying a three-dimensional sonic reflecting surface immersed in the liquid, it is necessary to provide means for measuring the intensity of elastic wave energy at a plurality of points in a matrix of points on a receiving surface. This invention is directed to the use of a simple, cheap means of indicating and/or recording the intensity of elastic wave energy at a plurality of points in such a medium. This invention involves the preplacement or predistribution of a material, called a detecting or receiving material, over an area comprising many wavelength in each of two perpendicular directions. At each point of placement of the detecting material, the state of distribution of the material is a function of the intensity of coherent elastic wave energy in the steady state wave pattern at that point. Thus, the intensity of elastic wave energy at each point can be determined from the state of distribution of the material after the initiation of irradiation of those points with elastic wave energy. The material can be finely divided solids, powders, encapsulated liquids, or liquid droplets immiscible with the liquid of the medium. The material can also be a liquid miscible with the liquid of the medium, but differing in some measurable characteristic, such as color, conductivity, etc. The material can also be a fluid in dynamic motion in the fluid of the medium, the characteristic motion being a function of the intensity of wave energy at the point. In each case, the state of distribution of the material will vary from the predistribution due to the particle motion of the medium during the irradiation of the point by the elastic wave field, and this variation will be a function of the intensity of the elastic wave field.

United States Patent [72] Inventor Daniel Silverman 5969 S. BirminghamSt., Tulsa, Okla. 74105 [21] Appl. No. 646,537

[22] Filed June 16, 1967 [45] Patented Apr. 27, 1971 Continuation-impartof application Ser. No. 512,689, Dec. 9, 1965, now Patent No. 3,400,363.

[54] METHOD AND APPARATUS FOR DETECTING COHERENT ELASTIC WAVE ENERGY2,525,873 10/1950 DeLano, Jr. 73/67 2,832,214 4/1958 Trommler 73/67.63,097,522 7/1963 Weller, Jr. 73/67 6 3,316,551 4/1967 Feder et 343/183,434,339 3/1969 Stetson et a1. 73/67.6

OTHER REFERENCES Mueller et al., Applied Physics Letters, Vol. 9, No. 9,Nov. 1, 1966, pp. 328- 329.

Primary Examiner-Richard A. Farley ABSTRACT: In the mapping of elasticwave fields in fluids, such as might be involved in recording a sonichologram in a liquid medium overlying a three-dimensional sonicreflecting surface immersed in the liquid, it is necessary to providemeans for measuring the intensity of elastic wave energy at a pluralityof points in a matrix of points on a receiving surface. This inventionis directed to the use of a simple, cheap means of indicating and/orrecording the intensity of elastic wave energy at a plurality of pointsin such a medium.

This invention involves the preplacement or predistribution of amaterial, called a detecting or receiving material, over an areacomprising many wavelength in each of two perpendicular directions. Ateach point of placement of the detecting material, the state ofdistribution of the material is a function of the intensity of coherentelastic wave energy in the steady state wave pattern at that point.Thus, the intensity of elastic wave energy at each point can bedetermined from the state of distribution of the material after theinitiation of irradiation of those points with elastic wave energy.

The material can be finely divided solids, powders, encapsulatedliquids, or liquid droplets immiscible with the liquid of the medium.The material can also be a liquid miscible with the liquid of themedium, but differing in some measurable characteristic, such as color,conductivity, etc. The material can also be a fluid in dynamic motion inthe fluid of the medium, the characteristic motion being a function ofthe intensity of wave energy at the point. In each case, the state ofdistribution of the material will vary from the predistribution due tothe particle motion of the medium during the irradiation of the point bythe elastic wave field, and this variation will be a function of theintensity of the elastic wave field.

PATENTED W27 :97:

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FIGJZ METHOD AND APPARATUS FOR DETECTING COHERENT ELASTIC WAVE ENERGYThis application is a continuation-in-part of my copending applicationSer. No. 512,689, entitled: Wavelet Reconstruction Process for Sonic,Seismic and Radar Exploration, filed Dec. 9, 1965, now U.S. Pat. No.3,400,363.

This invention relates to the nondestructive testing and mapping ofsingle or multilayered systems of elastic wave propagating media. Whilethis invention can be used for any type or size of solid or liquidsystem, it is particularly useful for exploring and mapping interfacesbetween organs in human or animal bodies. This invention is furtherdirected to methods of and apparatus for detecting and measuring theintensity of elastic wave energy in a standing wave coherent elasticwave field.

This invention utilizes the principles of optical holography. In thisprocess, a surface is irradiated with coherent luminous radiation of aspecific frequency. The luminous radiation is reflected and diffractedfrom the surface and is received at a photographic plate. In addition,part of the energy from the luminous source is reflected directly to thereceiving photographic plate where it combines with the radiationreaching the film from the surface. The combined radiation is thenrecorded on the film. The film is developed and is a hologram. Thisfilmcan be irradiated with coherent luminous radiation, and the light willbe diffracted by the holographic plate and will from an image of theoriginal irradiated surface.

In my copending application, Ser. No. 5 l2,689, entitled, WaveletReconstruction Process for Sonic, Seismic, and Radar Exploration," filedDec. 9, 1965, I describe sonic or seismic holographic systems. In thatapplication l show how a source of coherent elastic wave energy can beused to irradiate (for example) a solid surface immersed in a liquid.The elastic wave energy is reflected anddifi'racted from the solidsurface to a receiving array comprising an array of elastic wavereceivers. Part of the original radiation (or a second source ofradiation of the same frequency) is used to also irradiate thereceivers. The outputs of the receivers are amplified and recorded inthe form of spots, of selected optical properties. The positions of thespots on the record correspond to the positions of the correspondingreceivers in the receiving array. This record is a hologram. It, ora'reduced size transparency copy can be viewed in coherent illuminationto display the original irradiated reflecting and diffracting surface.

This present invention is an extension of the invention in Ser. No.5l2,689, and is concerned particularly with improved methods of andapparatus for detecting receiving and recording the elastic wave energyat the receiving points in the receiving plane or receiving surface.This invention isapplicable to the measurement of elastic wave energy influid media, either gas or liquid, and solid media for holographic orother purposes where the elastic wave field is a coherent steady statefield or standing wave field.

The conventional method of recording elastic wave energy is by the useof transducer instruments which are placed in or on thewave-transmitting medium and respond to the displacement, velocity, oracceleration of the particles of which the medium is composed, or thepressure within themedium.

These instruments normally generate small electrical voltages which mustbe amplified before being recorded. This requires a large amount ofexpensive equipment, particularly since many detecting points must beprovided in the receiver array.

Since the particles of the transmitting medium must move to transmit thewave motion, this invention makes use of this particle motion toredistribute a volume of detecting material placed in predistributedform in'oron the medium. Due to the wave motion, theparticles of themedium, as they move, will move and reposition the detecting material.Where the particle motion is greatest the repositioning will begreatest, and where the wave motion is least, the repositioningwill beleast.

For example, consider a liquid medium with the receiving material in afine powder capable of floating on the liquid surface, distributed moreor less uniformly over the surface. Where the particle motion is verylow, the material will not move appreciably. Where the particle motionis very high, the powder will be moved. In general, the powder will movelaterally toward and will accumulate at points of small particle motionand will move laterally away from points of large particle motion. Ifthe particles have a different optical property from the liquid medium,a photograph of the surface will show the resulting distribution of thematerial.

Instead of a receiving material being solid, such as powders, particles,or encapsulated materials, it may be a liquid of properties contrastingwith those of the liquid medium in which it is placed. Thus a small dropof salt water placed at a point on the surface of a quiescent body offresh water will stay essentially fixed, although, it will start toslowly diffuse through the water. However, if an elastic wave shouldmove past the point, the resulting motion of the water particles willcause some turbulence and mixing of the salt water and the water of themedium causing a more rapid movement of the salt water away from thepoint. This movement can be detected electrically.

The receiving material can be a water-soluble dye of contrasting colorto that of the water of the medium or a fluorescent dye, for example.Then the resulting distribution of the dye can be observed optically orphotographed for a record, and so on.

The principle object of this invention, therefore, is to provide asimple, cheap, and easily handled detecting means to detect, measure,and/or record the steady state standing elastic wave energy field in anelastic wave energy transmitting medium.

Still other objects and details of this invention will become evident inconnection with the following drawings and description of a number ofembodiments of my invention in which:

FIG. I and 2 illustrate schematically one embodiment of this inventionin which conventional transducer devices are used to initiate and detectthe elastic wave energy.

FIGS. 3, 4a, and 4b illustrate the application to this type of systemthe use of one type of detecting system employing a particulatematerial.

FIG. 5 illustrates a modification of the system of FIG. 3.

FIG. 6 illustrates a type of detector in which the detecting material isa liquid in a liquid medium.

FIGS. 7a and 7b illustrate two types of arrays of detectors of the typeillustrated in FIG. 6.

FIG. 8 illustrates schematically another embodiment in which thedetecting material is a liquid flowing in conjunction with a secondliquid with which it is miscible.

FIG. 9 illustrates schematically an embodiment in which detectingmaterial is a liquid of the same nature as the liquid of which themedium is constituted.

FIG. 10 illustrates a type of indicator useful in connection with thesystem of FIG. 9.

FIG. 11 illustrates a method of creating a frequency-sensitive detectorsystem employing the principles of FIGS. 6, 8 and 9, etc.

FIG. 12 illustrates an embodiment in which two liquid media are used andthe interface between them becomes a reflectormeans for holographicpurposes.

In FIG. I, I show a method of recording a hologram of a solid surfacesubmerged in a liquid medium. This surface can be the exterior surface(or an interior surface) of a human or animal body, or other solid orliquid single or multielement system. The portion of the body 10 to bemapped is placed in contact with a layer of liquid 12 within anenclosure 11. This can be a fencelike enclosure resting on top of thebody, sealed along edges 13, I4, for example. Or the body or the part ofit to be examined, can be immersed in a tank of liquid, such as water.The liquid can be below, to the side of, or above the body, In FIG. I,the water overlays the body and the surface of the water is shown at 15.

A transducer 16 is supplied with electric power of a constant frequency,f, from an oscillator 18 through amplifier 19. This sets up an elasticwave field (EWF) in the water. As shown in FIG. 2, which is a sideelevation of FIG. 1, part of this elastic wave energy (EWE) is reflectedby reflecting surface 25 to the surface 15 of the water. Part of the EWEfrom transducer 16 is directed to the outer surface 26 of the body andis reflected and diffracted, or otherwise redirected, to the surface ofthe liquid 15, where it combines with the EWE from reflector 25 toprovide a resulting steady state EWF at the surface.

This field can be explored by a conventional transducer 17 immersed inthe liquid 12 near the surface 15. It is connected to an amplifier 20and cathode ray tube (CRT) 21 where the beam spot is brightened inaccordance with the strength of the signal picked up by 17, and thusproportional to the intensity of the EWF at the point where thetransducer is positioned. The transducer is adapted to be moved to aplurality of points 28 in an array in the receiving surface. At the sametime, by means not shown but well know, the spot on the CRT is made tomove in a corresponding array. The resulting pattern of spots on theface of the CRT is imaged by lens 22 onto a photographic plate or film23. The developed plate 23 is a hologram of the surface 26.

It is time consuming to reposition the receiving transducer to aplurality of points 28. So a plurality of transducers 17 could bepositioned, one at each of the points 28, each connected to an amplifierand to an optical transducer, and so on. However, this inventionprovides a much simpler, faster, and cheaper method of making a recordof the EWF at the receiving surface.

This is illustrated in flG. 3. This shows a tank 1 l with water 12, tolevel and a three-dimensional object 30 immersed in the water. Thetransducer 16 irradiates the surface of object 30 with coherent EWE. Inaddition, there is a reflector surface, like 25 of FIG. 2, (not shown)that reflects part of the EWE from 16 up to the surface. At the surface15 of the liquid 12 the two sets of coherent waves combine to form aresultant steady state standing wave EWF.

A material, such as a fine powder, like lycopodium powder, for example,or other fine particulate matter 31 of less density than water, isspread over the surface 15, in a more or less uniform distribution. Theactual distribution is not too critical, as will be seen.

When an EWF is set up in the liquid (water) it is transmitted by themovement of particles of the water under the influence of the EWF. Atthe surface, the particle motion of the water will be greatest where theintensity of the EWF steady state standing wave pattern is greatest. Andthe particle motion will be least where the amplitude or intensity ofthe EWF is least. Where the particle motion of the water is high, thepowder floating on the surface will be disturbed by the water particlemotion and will move laterally to positions of lower intensity ofmotion. Thus, after a suitable period of time, which would be probablyquite short, the powder will accumulate in those parts of the surfacewhere the intensity is least, and there will be little or no powderwhere the intensity of the particle motion is highest. The resultingpattern or state of distribution of the powder 31 over the surface afterthe passage of the EWE can be recorded by means of a camera 34 with lens36 and film 35. The surface 15 can be illuminated by lamp 32. Of course,the optical properties of the powder and of the liquid must be differentso that the resulting photograph will have areas of contrasting densitycorresponding to the areas of powder and liquid. This photograph is ahologram of the sur-.

face of object 30, and an image of the surface can be reconstructed bythe well-known methods of optical holography.

Instead of a naturally occurring powder or fine seed, it is possible togrind a solid material of low density such as cork, for example. Thesize of the particles should be small compared to the wavelength of theEWE in the liquid. For long wavelengths, the particles could be larger,for example, pingpong balls, or the like.

If a plane wave of EWE intersects surface 15 at a large angle, the nodesand antinodes, or points of low and high particle motion, will be in theform of parallel lines,'separated by a distance of somewhat less thanthe wavelength. Thus, to accurately map this EWF, it is necessary thatthe points at which measurement of the EWF intensity are made be spacedat distances of less than a wavelength and preferably less than one-halfwavelength.

In FIG. 4a, I show how in the case of a single liquid medium 12 in acontainer 11, the powder 31 can be supported on the free surface 15. InFIG. 4b, Ishow how a double liquid system can be used in which a lessdense liquid 12a overlies the liquid 12 in which the object is immersed.The powder can be placed on the free surface 15 or the intermediatesurface 15a between liquids l2 and 12a.

In the case of very high frequency waves in a liquid medium, (that is,very small wavelength) the entire holographic picture, covering manywavelengths in each direction, can be indicated on a water surface ofrelatively small area. However, with low frequencies, such as in sonicsignalling in water, the wavelength may be many tens of feet and theentire surface of interest may be hundreds or thousands of feet across.In such a case it would be difficult to examine or photograph such alarge surface at one time. However, it is possible to map the largesurface by providing a matrix of point indicators. Each of theseindicators will indicate a function of the intensity of the EWF overlocal areas surrounding the points.

FIG. 5 illustrates one type of indicator. It comprises a container 40with open bottom covered by a thin flexible membrane 41, fastened bymeans 42. The top 50 is transparent and sealed. The indicator can beimmersed partially or totally in the medium. There is an air space 43above the liquid 44, with a free surface 45. The liquid 44 can be thesame as or different from the medium 38. The powder 52 is on the freesurface and is originally placed in substantially uniform spacing on thesurface. If the device 39 is put into the EWF in the medium at a pointwhich is an antinode, the powder will be driven away, that is, driventoward the walls of the container 40 and the center will besubstantially clear. On the other hand, if the device 39 is placed at anode in the medium, there will be little or no tendency for the powderto move at all, and its distribution will not change appreciably. Atintermediate points in the EWF the action will be intermediate.

These conditions can be determined by manually viewing, or byphotographic or photoelectric means. This can be done by means of lamp53, and PE cell 55. The change in light transmission through the layerof opaque powder on the liquid will be indicative of the action of thepowder, and thus of the intensity of EWE at the point of placement ofthe device 39.

The'material that is placed in or on the EWE medium can be a solid infinely divided form, or it can be fine droplets of liquid immisciblewith the liquid of the medium, such as a fine mist of oil (in a watermedium). It can also be minute capsules of a liquid in a solidencapsulation. These would act essentially as the powder described inconnection with FIGS. 3, 4, and 5. The material can also be a solidmaterial which is slowly soluble in the liquid medium. The rate ofsolution will be a function of the intensity of the EWE.

If the material is a layer of fine droplets of oil, for example,floating on the water, the action of the EWE reaching the receivingsurface (or receiving plane) might be to cause the droplets to coalesceinto larger droplets. The extent of this action would be a function ofintensity of the EWF. The nature of the distribution of the material,such as fine droplets, larger droplets, or very large droplets, etc.,would be indicative of the intensity of the EWF.

There is another form in which an indicator material can be used. Thisis illustrated in FIG. 6. The medium 60 can be a liquid such as water. Aprobe 62 is arranged (either by means of a hollow conduit, or smallreservoir 61) to hold a miscible liquid of differing physiochemicalproperties than the liquid 60. This can be a conductive liquid, forexample, or a colored or opaque dye, etc. Consider that the reservoir 61holds a conduetive liquid such as a salt solution. The screen or barrier64 can be a conductive shell or wire, etc., surrounding the probe. Abattery 65 and resistor 66 are connected between the probe and thebarrier. A potential indicator 67 is also connected between the probeand the barrier.

At the start, when a droplet of liquid is placed by the probe 62 intothe liquid 60 at point 6], nothing happens. There is an open circuitbetween the probe and the barrier, and the indicator 67 will show thepotential of the battery 65. The salt solution will begin to diffusethrough the liquid 60 toward the barrier. However, this is a very slowprocess. On the other hand, a high intensity of EWE in the area of theprobe will cause turbulence in the liquid and mixing of the liquid 60and the salt solution. Therefore, very quickly the conductive saltsolution will reach the barrier, and the potential of the probe (withrespect to the barrier) will drop to a value indicative of the relativevalues of resistor 66 and the resistance of the path between 61 and 64.This potential will be a measure of the EWF intensity.

The system shown in FIG. 6 is adaptable to a multiple array such asshown in FIGS. 7a and 7b. Multiple probes 62 and barriers 64 are placedin a two-dimensional matrix of rows 73 and columns 72. The barriers canbe cylinders of perforated metal or screen. Or they can be formed ofinterconnecting sets of wires in rows and columns 82 and ill. Screen orhardware cloth could be used for this purpose. These would be groundedtogether 74 and connected to a battery 75. The other pole of the batterywould be connected through resistors 76 to the probes 62.

The barriers 64 or wires 81, 82, can be mounted to an insulated frame,which also holds the probes. This framework is not shown but would beknown to one skilled in the art.

The indicators, like 67, can be manually read. Or the voltage betweenprobes and barriers can be recorded by multielement oscillographs orrecords. Or the voltages can be multiplexed and recorded. Or they can berecorded directly as shown in FIG. 6. Here a metal plate 69 is mountedabove the probe and barrier. It is connected to the ungrounded pole ofthe battery 65. The potential between probe 62 and plate 69 is thepotential across the resistor, which is zero until there is conductivitybetween probe and barrier. The sum of indicator voltages 67 and 79 is,of course, the battery potential. 80 as indicator 67 voltage drops, thevoltage of 79 will rise.

An electrographic sheet 70, such as facsimile paper, etc., is placed ontop of plate 69. The probe 62 pierces the sheet (and therefore iselectrically connected to it). The plate 69 has an opening 71surrounding the probe. So the sheet experiences the potential betweenprobe and battery. The darkening of the sheet 70 due to this potential,is a measure of the potential and thus of the intensity of the EWF. Theplate 69 and sheet 71 can, of course, be adapted to the matrix of FIG.7. In such a case, the sheet would show a pattern of dark and lightpatches. It, or a reduced size transparency of this sheet would be ahologram of the EWF at the surface of the irradiated object.

The receiving surface is the surface defined by the array of probes andbarriers or screens. This can be a plane, horizontal or tilted, or itcan be a curved surface.

If the receiving material is a dye miscible with the medium liquid, thisdroplet of dye will remain at the location of the probe. However, whenthe EWE reaches the receiving surface, the turbulence causes mixing ofthe dye and the water. The spreading of the color, that is, the radiusof the dye patch, as a function of time, is a measure of the intensityof the EWF. A photograph of the dye patches will be a hologram. Asuccession of photographs can be taken at increasing time intervals, andthe progress of the dye noted as a measure of the EWF intensity. Theaction of the mixing is progressive. In other words, the total mixingand spread of the dye is, in effect, a time integration of the particlemotion of the liquid. Thus, this method can be utilized for recordingweak EWF.

If desired, a photoelectric system such as shown in FIG. 5, can be usedwith an opaque dye to record the progress of the mixing and dispersionof the dye.

The assembly of probe 61 and barrier 64 of FIG. 6 could, of course, beadapted to the assembly of FIG. 5, for example. The wall 40 wouldcorrespond to the barrier, and the probe would be mounted in the centerof the container. The use of the membrane 41 (for transmission of thewave motion) would permit using a liquid of different properties 44inside the device 39 than the liquid of the medium 38. The presence ofthe membrane and closed container 44 isolates the detection or receivingmaterial against constant flow currents in the medium 38.

There is another form in which the material can be applied to themedium. This is shown in FIG. 8. Here, I use a short length 87 of thinflexible tubing. It is supported by spaced pipes 88, 89, held in fixedrelative position by means not shown. A nonconducting liquid is flowedinto pipe 88, through tubing 87 and out of pipe 89. The rate at whichthis liquid flows is such as to cause streamlined flow in 87. A separatesmall pipe 92 passes through pipe 88 at 93 and is positioned along theaxis of tubing 87. A conducting wire 96 is passed through pipe 92 andextends along the axis. A screen or nonconducting surface is placed onor near the inner surface of the tubing 87. A battery 98 and indicator197 are connected between wire 95 and screen 97.

As the receiving material, salt water, for example, flows into 92 whilefresh water flows into 90, a streamlined flow occurs with a central coreof conducting water in a flowing column of nonconducting water. If thereis no turbulence there will be substantially no conductivity betweenwire 95 and screen 97 and no current through indicator 197. However, ifthis assembly is immersed in an EWF in the medium 60, the particlemotion in the medium will be communicated through the tubing 87 to theliquid therein. This will cause a turbulent flow and mixing of the saltand fresh water and conductivity between wire and screen. This mixingwill be a function of the diameter and length of the tubing 87, thelength of wire 95, the flow rate of liquid and receiving material, thelength of pulse of receiving material, and the intensity of the EWF. Bycontrol of these variables an indication of the function of theintensity of the EWF can be had. If the liquid 90 and medium 60 are bothnonconducting, it would not be necessary to use the flexible plastictube 87.

Multiple units like that in FIG. 8 can be used in an array as in FIG. 7.This assembly or array of units like FIG. 8 can be placed in a plane orcurved receiving surface, in any position or attitude within the EWEtransmitting medium. If a dye solution is used in pipe 92, the mixing ofdye and liquid can be observed or recorded optically. The tubing 87 can,of course, be a circular or rectangular cross section channel (betweentwo parallel plastic surfaces). Other materials and physiochemicalproperties can, of course, be used. Also, the flow of liquids into pipes88 and 92 (90, 67) can be controlled from a pipe manifold by means offlow resistance pressure dropping units such as fine bore tubes ororifices, not shown, but well known in the art.

In FIG. 9, I show another type of fluid turbulence detector that can beused to indicate the presence and/or intensity of EWE at a point in afluid. While any fluid medium can be used, that is, gas, or liquid, itsoperation will be described in terms of a liquid such as water. Itcomprises a pair of fine tubes 110, 111, which are held in rigidrelative position so that they are exactly coaxial 112 and spaced aparta distance 109. They can be held by means such as bracket 113 withclamps 114. The assembly is placed with the gap at point 108 in medium115 at the desired depth.

Water is introduced under pressure at 117 and flows along the axis 112from tube 110 to tube 111 and creates a flow out of 111 at 123. The flowmust be at such a rate that it is streamlined from 110 to 111. If theflow is turbulent, the amount of flow reaching 123 will be reduced.Also, if some outside disturbance such as an EWF should flow acrosspoint 108, and if it is of sufficient intensity, it will cause astreamlined flow from 110 to 111 to become turbulent. Thus, the flow 125at I23 will become less, and this reduction in flow is an indication ofthe EWF.

I show a fluidic amplifier 118 comprising a chamber 126, fluid input119, outputs 120 and 121 and control inputsl22, 123. Some of the inputfluid from 119 is bypassed 124 to 122. This causes the stream of liquid(in this case, water) from 119 to flow out leg 121. when water flows intube 110 at 117 and in streamlined flow from 110 into 111 and 123, then,if this control flow is greater than the control flow at 122, the streamwill switch from 121 over to and flow out of leg 120.

So long as conditions at 108 remain streamlined, the flow from 119 willgo to leg 120. However, if anything should disturb the flow at 108 andmake it turbulent (such as by EWE), then the flow at 123 will be reducedand the flow from 119 will switch to leg 121. This switch from 120 to121 is an on-off indicator of energy intensity in the EWF at 108. Ofcourse, the output of fluidic amplifier 1 18 can be used to drive otherstages of fluidic amplifier. Or the output of 118 can be used to controla relay to make an electrical circuit or it can be used to drive afluidic indicator.

One useful type of indicator is shown in FIG. 10. It comprises asmall-diameter tube 130 closed off at top with a transparent wall. Inputpipe at bottom 132 comes from one of the legs 120 or 121. A colored ball134, which is a close, but not tight, fit into the tube is placed insidethe tube. When fluid enters the tube at 132 the ball is raised to thetop, shown dotted as position 134, where it can readily be seen throughthe window 131. A fluid output 133 with some flow resistance, provides ameans for fluid bypass. When the flow at 132 stops, the ball drops back.The ball could also be a short cylinder or plunger. The indicator can betied to either leg 120 or 121, since when flow in one leg stops, itstarts in the other, and vice versa.

A plurality of turbulence indicators 107 can be used with fluidicamplifiers 118 and flow indicators 135. The turbulence indicators 107would be placed in a matrix array. The flow indicators 135 would be in acongruent array. A photograph of the array of flow indicators in aclosely packed array would show a pattern of contrasting patches. Thiswould be a hologram of the submerged surface sending reflections anddiffractions to 107 from a coherent source of EWE. If the flow in pipe123 is great enough the indicator 135 could be connected directly to 123instead of through amplifier 118.

In FIG. 9, I show a liquid jet from pipe 110 impinging on pipe 111. Ifthe liquid medium in which the pipes are immersed is quiescent, the jetflow will be streamlined along the axis of the pipes 110, 111. However,if there is particle motion in the liquid due to elastic wave motion,this jet flow will be disturbed. A constant current in the liquid (a DCsignal) or a fluctuating motion (an AC signal) will both disturb thejet.

Since the EWE in holography is a constant frequency AC signal, I find itadvantageous to make my detector system, the pipes 110, 111, and otherapparatus of FIG. 9, sensitive only to alternating particle motion of apredetermined frequency, which is that of the EWF. I do this by placingthe jet transverse to the axis of a Helmholtz resonator 140, FIG. 11.The pipes 144, 145, are placed in the neck-142, where the motion of theliquid is in the direction of the axis 146 of the neck of the resonator.The amplitude of the pulsation of liquid in the neck of the resonatoris, of course a function of the EWF and the frequency. When thefrequency of the signal is the same as the resonant frequency of thecavity, there will be a maximum response and a maximum sensitivity ofthe detector. When the frequencies are different, there will be aminimum of sensitivity. This is, of course, ideal since we are using aconstantfrequency signal to irradiate the hidden surface and the tuneddetector tends to discriminate against noise, that is, any particlemotion in the liquid of difi'erent frequencies due to any other sources.

When there is particle motion in the liquid in which the resonatordetector 140 is immersed, the oscillatory particle motion in the neck142 will cause turbulence and will break up the streamlined motion ofthe jet from 145 to 144. The sensitivity of this detector is a functionof the diameter of the pipes 145, 144 and their spacing. The shorter thespacing, the more stable the jet and the less sensitive the detector,and so on. The sensitivity also depends on the design of the resonator,

in the sense of the amplitude of oscillation of the liquid in the neck.This art is well known.

While I have shown in the resonator of FIG. 11 the detecting means ofFIG. 9, it is equally possible to apply to this resonator system othertypes of detectors, such as those shown in FIGS. 6 and 8, for example,and others. Also, the systems of FIG. 11, and FIG. 9, while described interms of a liquid medium, could equally well be used in a gaseousmedium.

In FIG. 3, I show a pattern of particles 31 on the liquid surface 15,and a lamp 32 to illuminate the surface and a camera 34 or other deviceto record the pattern of the patches of material. This photograph is ahologram of the irradiated submerged surface. However, the surface 15,with material 31, forming a pattern of light, shade, or color, is also ahologram. Thus, by substituting a coherent beam of light in place oflamp 32 to illuminate the surface 15, and by placing the camera 34 inthe proper position, as is well known in optical holography, the camerawill photograph a reconstructed image of the hidden surface. This sametechnique can also be used with the sheet 70 of FIG. 6 and other similarembodiments.

In FIG. 4b, I show an embodiment in which a body might be submerged in afirst liquid 12, with a second liquid 12a of less density placed abovethe liquid 12. The detecting material can be placed in the interfacebetween the two liquids, or on the surface of the upper liquid. In FIG.12, I show a further modification of this embodiment in which thematerial 31 is placed on the surface of liquid 12a. The source ofcoherent elastic wave energy 16 is immersed in the top liquid 12a and bymeans of rays illustrated schematically as irradiates the upper surface26 of body 10 placed in the lower medium 12. Some of these rays 150 willbe reflected upwardly by interface 153, as rays 151 to the surface andthe array of detecting material 31. Others of the rays will project intothe second medium 12 and to the body and be reflected from the surface26, and thence upwardly as 152 to the surface 15. If the interface 153between the two liquids is a plane surface (that is, without substantialripples, etc.) the rays reflected upwardly will serve as a biasing EWF,similar to that provided by means of reflector 25 of FIG. 2. Thus, thecombination of the two EWF, that reflected from the interface 153 andthat from the surface 26 will combine to form a combination EWF at thesurface 15 that will change the state of distribution of the material 31to form a hologram of the submerged surface 26. g In my copendingapplication, Ser. No. 512,689, I show, in FIG. 8 therein, how it ispossible to use two separate areas or patches of receivers, withcorresponding means to make two areas or patches of luminous spots andtwo resulting holograms. The two records or holograms would correspondto the two separated receiving areas, and would, when the wavefrontswere reconstructed, show two images of the hidden surface as seen fromtwo different angles. These two images would fon'n a stereo-opticalpair, and by well-known means, could be used to determine size andposition of the hidden surface with respect to the geometry of the tworeceiving areas and the optical system.

In this invention, I plan to incorporate the same feature. For example,in FIG. 3, I propose the use of two separated receiving surfaces withreceiving material distributed as two separated patches 31, 31' in thereceiving surfaces. The camera 34 would then be used to record the stateof distribution of the receiving material in these two patches 31, 31 onthe surface 15 of the liquid. The two resulting photographs or hologramswould then (when properly irradiated with coherent illumination) formtwo images of the body 30, and photographs of these images would formthe desired stereo arr.

While I call for two separate sources of coherent elastic wave energy ofthe same frequency, these can comprise, as shown in FIGS. 2 and 12, onetransducer source 16 and a reflector source 25 and 153, respectively, orit can comprise two separate transducer sources as shown in my US. Pat.No. 3,400,363, FIG. 6, one of which irradiates the object and the otherof which irradiates the receiver surface.

While my invention has been described with reference to the foregoingspecial embodiments and illustrations, it will be apparent to thoseskilled in the art that the principles of the invention can be employedto accomplish its objects in many further and different ways notdisclosed in detail. Also, different language may be used to describethese embodiments. For example, when I speak of in the medium" orimmersed in the medium," I mean positioned inside the volume of themedium or on an exterior surface of the medium. The scope of theinvention should, therefore, not be construed as limited to theembodiments and details described, but it is preferably to beascertained from the scope of the appended claims.

lclaim:

1. Apparatus for detecting interfering coherent elastic wave energy inan elastic wave transmitting medium, comprising:

a. at detecting material,

b. means for distributing said detecting material in a predeterminedmanner in the vicinity of at least one point in a receiving surface insaid medium,

c. The state of distribution of said detecting material in said mediumadapted to be changed by the physical lateral movement of said materialdue to the movement of the particles of said medium as the result of acoherent standing elastic wave pattern at said receiving surface,

d. means for initiating the irradiation of said at least one point withcoherent elastic wave energy of a frequency f from a first sourcethereof,

e. means for initiating the irradiation of said at least one point withcoherent elastic wave energy of frequency f from a second sourcethereof, whereby a steady state standing wave pattern of coherentelastic wave motion is set up in the vicinity of said first point, and

f. means for detecting a function of the state of distribution of saidmaterial at said at least one point after the initiation of saidirradiations.

2. Apparatus as in claim 1 in which said medium is a first liquid, andsaid material is a second liquid.

3. Apparatus as in claim 1 which said state of distribution of saidmaterial is static.

4. Apparatus as in claim 1 in which said state of distribution of saidmaterial is dynamic.

5. Apparatus as in claim I in which said receiving surface is a planesurface.

6. Apparatus as in claim 5 in which said medium is a solid, saidreceiving surface is an external surface of said medium, and saidmaterial is positioned on said external surface of said medium.

7. Apparatus as in claim 1, in which said means for initiatingirradiation comprises a source of coherent elastic wave energy of afrequency f irradiating a second surface immersed in said medium, saidsecond surface adapted to redirect to said at least 'one point part ofthe coherent elastic wave energy it receives.

8. Apparatus as in claim 7 including also the direct irradiation of saidat least one point by coherent elastic wave energy of frequency f.

9. Apparatus as in claim 1 in which said material is a particulatematerial.

properties of said medium and means to photograph said receiving surfacewith said material thereon.

11. Apparatus as in claim 2 in which said second liquid is a conductingliquid and said medium is a nonconducting liquid and said means todetect a function of the state of distribution of said materialcomprises means for measuring a function of the conductivity of saidmedium in the vicinity of said at least one point in said receivingsurface.

12. Apparatus as in claim 11 in which the means to measure said functionof the conductivity of said medium comprises means for applying anelectrical potential to said at least one point and means for measuringa function of the current flowing from said point to an adjacentconductor in said medium.

13. Apparatus as in claim 12 in which said function of said current isrecorded by electrographic means.

14. Apparatus as in claim 2 in which said second liquid is a dye ofcontrasting optical properties to those of said first liquid.

15. Apparatus as in claim 14 in which the function of the state ofdistribution of said second liquid is measured by optical means.

16. Apparatus as in claim 2 in which said second liquid is in dynamicstreamlined fiow inside said first liquid prior to the initiation ofirradiation by elastic wave energy and in turbulent flow after saidinitiation of irradiation.

17. Apparatus as in claim 1 including at least one resonant cavity tunedto the frequency of said elastic wave energy placed at said at least onepoint.

18. In a coherent elastic wave apparatus in which a source of coherentelastic waves irradiates a hidden object surface submerged in a firstelastic wave transmitting medium, and in which elastic waves redirectedby said hidden object surface are received by a receiver system arrayedin a receiving surface in a second elastic wave transmitting medium inelastic wave transmitting contact with said first medium and with saidhidden object surface, the improvement comprising,

a receiver material, said material positioned in a predetermineddistributed array in said receiving surface,

the state of distribution of said material adapted to be changed by thephysical lateral movement of said material due to the movement of theparticles of said second medium in which said array is positioned as theresult of a coherent elastic steady state standing wave pattern at saidreceiving surface,

means to initiate the irradiation of said hidden object surface withcoherent elastic wave energy of frequency f from a first source thereofat least part of which is redirected to said receiving surface,

means to initiate the irradiation of said receiving surface withcoherent elastic wave energy of frequency f from a second sourcethereof, whereby a steady state standing elastic wave pattern is formedat said receiving surface, and

means to detect a function of the state of distribution of said materialover said receiving surface after the initiation of said twoirradiations.

19. Apparatus as in claim 18 in which said means to irradiate saidreceiving surface comprises a separate means from the means whichirradiates said hidden object surface.

20. Apparatus as in claim 18 in which the same means is used tosimultaneously irradiate both said receiving surface and said hiddenobject surface.

21. Apparatus as in claim 18 in which both said first medium and asecond medium in contact with said first medium are liquids.

22. Apparatus as in claim 2] in which said receiving surface is in theinterface between said first medium and said second medium.

23. Apparatus as in claim 21 in which said receiving surface is in saidsecond medium.

24. Apparatus as in claim 17 in which said first medium is a solid, saidsecond medium is a liquid in contact with said solid and said receivingsurface is in said liquid.

25. Apparatus as in claim 17 in which said array comprises atwo-dimensional matrix of spaced detecting points.

26. Apparatus as in claim 25 in which the spacing between said points isless than one wavelength of said elastic waves in said medium.

27. Apparatus as in claim 25 in which the spacing between said points isless than one-half wavelength of said elastic waves in said medium.

28. Apparatus as in claim 18 in which said predetermined distributedarray in which said material is positioned in said receiving surfaceincludes at least two spaced patches of material.

29. In a coherent elastic wave apparatus in which a first source ofcoherent elastic wave energy of frequency f irradiates a first surfacesubmerged in a first elastic wave transmitting medium and in whichelastic waves redirected by said first surface are received in part by areceiver system arrayed in a receiver surface in an elastic wavetransmitting medium in elastic wave transmitting contact with said firstsurface, and a second source of coherent elastic wave energy offrequency f irradiates said receiver surface, the method of detectingthe coherent elastic standing wave pattern formed at said receiversurface comprising the steps of,

a. placing a receiver material in a predetennined distribution over atleast part of said receiver surface, the state of distribution of saidmaterial adapted to be changed by the physical lateral movement of saidmaterial due to the movement of the particles of said medium in whichsaid material is positioned as the result of a coherent elastic standingwave pattern at said receiving surface,

b. irradiating said first surface by said first source whereby part ofthe energy received by said first surface will be redirected to saidreceiver surface,

c. irradiating said receiver surface by said second source,

whereby said standing wave pattern will be set up, and

d. detecting a second state of distribution of said receiver material insaid receiver surface after said irradiations.

30. The method of claim 29 in which a single transducer of coherentelastic wave energy provides both said first and said second sources ofcoherent radiation.

31. The method as in claim 29 including the step of making a record ofsaid second state of distribution of said receiver material in saidreceiver surface.

32. The method as in claim 31 including the steps of making a reducedsize transparency of said record and irradiating said transparency withcoherent luminous radiation, whereby an image of said first surface willbe reconstructed.

33. The method as in claim 29 including the step of irradiating saidsecond state of distribution of said receiver material in said receiversurface with coherent luminous radiation, whereby an image of said firstsurface will be reconstructed.

34. The method as in claim 29 in which said step of placing saidreceiver material comprises placing said material in at least two spacedpatches in said receiver surface.

1. Apparatus for detecting interfering coherent elastic wave energy inan elastic wave transmitting medium, comprising: a. a detectingmaterial, b. means for distributing said detecting material in apredetermined manner in the vicinity of at least one point in areceiving surface in said medium, c. The state of distribution of saiddetecting material in said medium adapted to be changed by the physicallateral movement of said material due to the movement of the particlesof said medium as the result of a coherent standing elastic wave patternat said receiving surface, d. means for initiating the irradiation ofsaid at least one point with coherent elastic wave energy of a frequencyf from a first source thereof, e. means for initiating the irradiationof said at least one point with coherent elastic wave energy offrequency f from a second source thereof, whereby a steady statestanding wave pattern of coherent elastic wave motion is set up in thevicinity of said first point, and f. means for detecting a function ofthe state of distribution of said material at said at least one pointafter the initiation of said irradiations.
 2. Apparatus as in claim 1 inwhich said medium is a first liquid, and said material is a secondliquid.
 3. Apparatus as in claim 1 which said state of distribution ofsaid material is static.
 4. Apparatus as in claim 1 in which said stateof distribution of said material is dynamic.
 5. Apparatus as in claim 1in which said receiving surface is a plane surface.
 6. Apparatus as inclaim 5 in which said medium is a solid, said receiving surface is anexternal surface of said medium, and said material is positioned on saidexternal surface of said medium.
 7. Apparatus as in claim 1, in whichsaid means for initiating irradiation comprises a source of coherentelastic wave energy of a frequency f irradiating a second sUrfaceimmersed in said medium, said second surface adapted to redirect to saidat least one point part of the coherent elastic wave energy it receives.8. Apparatus as in claim 7 including also the direct irradiation of saidat least one point by coherent elastic wave energy of frequency f. 9.Apparatus as in claim 1 in which said material is a particulatematerial.
 10. Apparatus as in claim 9 in which said means to detect afunction of the state of distribution of said material comprises amaterial of optical properties contrasting with the optical propertiesof said medium and means to photograph said receiving surface with saidmaterial thereon.
 11. Apparatus as in claim 2 in which said secondliquid is a conducting liquid and said medium is a nonconducting liquidand said means to detect a function of the state of distribution of saidmaterial comprises means for measuring a function of the conductivity ofsaid medium in the vicinity of said at least one point in said receivingsurface.
 12. Apparatus as in claim 11 in which the means to measure saidfunction of the conductivity of said medium comprises means for applyingan electrical potential to said at least one point and means formeasuring a function of the current flowing from said point to anadjacent conductor in said medium.
 13. Apparatus as in claim 12 in whichsaid function of said current is recorded by electrographic means. 14.Apparatus as in claim 2 in which said second liquid is a dye ofcontrasting optical properties to those of said first liquid. 15.Apparatus as in claim 14 in which the function of the state ofdistribution of said second liquid is measured by optical means. 16.Apparatus as in claim 2 in which said second liquid is in dynamicstreamlined flow inside said first liquid prior to the initiation ofirradiation by elastic wave energy and in turbulent flow after saidinitiation of irradiation.
 17. Apparatus as in claim 1 including atleast one resonant cavity tuned to the frequency of said elastic waveenergy placed at said at least one point.
 18. In a coherent elastic waveapparatus in which a source of coherent elastic waves irradiates ahidden object surface submerged in a first elastic wave transmittingmedium, and in which elastic waves redirected by said hidden objectsurface are received by a receiver system arrayed in a receiving surfacein a second elastic wave transmitting medium in elastic wavetransmitting contact with said first medium and with said hidden objectsurface, the improvement comprising, a receiver material, said materialpositioned in a predetermined distributed array in said receivingsurface, the state of distribution of said material adapted to bechanged by the physical lateral movement of said material due to themovement of the particles of said second medium in which said array ispositioned as the result of a coherent elastic steady state standingwave pattern at said receiving surface, means to initiate theirradiation of said hidden object surface with coherent elastic waveenergy of frequency f from a first source thereof at least part of whichis redirected to said receiving surface, means to initiate theirradiation of said receiving surface with coherent elastic wave energyof frequency f from a second source thereof, whereby a steady statestanding elastic wave pattern is formed at said receiving surface, andmeans to detect a function of the state of distribution of said materialover said receiving surface after the initiation of said twoirradiations.
 19. Apparatus as in claim 18 in which said means toirradiate said receiving surface comprises a separate means from themeans which irradiates said hidden object surface.
 20. Apparatus as inclaim 18 in which the same means is used to simultaneously irradiateboth said receiving surface and said hidden object surface. 21.Apparatus as in claim 18 in which both said first medium and a secondmedium in contact with said firsT medium are liquids.
 22. Apparatus asin claim 21 in which said receiving surface is in the interface betweensaid first medium and said second medium.
 23. Apparatus as in claim 21in which said receiving surface is in said second medium.
 24. Apparatusas in claim 17 in which said first medium is a solid, said second mediumis a liquid in contact with said solid and said receiving surface is insaid liquid.
 25. Apparatus as in claim 17 in which said array comprisesa two-dimensional matrix of spaced detecting points.
 26. Apparatus as inclaim 25 in which the spacing between said points is less than onewavelength of said elastic waves in said medium.
 27. Apparatus as inclaim 25 in which the spacing between said points is less than one-halfwavelength of said elastic waves in said medium.
 28. Apparatus as inclaim 18 in which said predetermined distributed array in which saidmaterial is positioned in said receiving surface includes at least twospaced patches of material.
 29. In a coherent elastic wave apparatus inwhich a first source of coherent elastic wave energy of frequency firradiates a first surface submerged in a first elastic wavetransmitting medium and in which elastic waves redirected by said firstsurface are received in part by a receiver system arrayed in a receiversurface in an elastic wave transmitting medium in elastic wavetransmitting contact with said first surface, and a second source ofcoherent elastic wave energy of frequency f irradiates said receiversurface, the method of detecting the coherent elastic standing wavepattern formed at said receiver surface comprising the steps of, a.placing a receiver material in a predetermined distribution over atleast part of said receiver surface, the state of distribution of saidmaterial adapted to be changed by the physical lateral movement of saidmaterial due to the movement of the particles of said medium in whichsaid material is positioned as the result of a coherent elastic standingwave pattern at said receiving surface, b. irradiating said firstsurface by said first source whereby part of the energy received by saidfirst surface will be redirected to said receiver surface, c.irradiating said receiver surface by said second source, whereby saidstanding wave pattern will be set up, and d. detecting a second state ofdistribution of said receiver material in said receiver surface aftersaid irradiations.
 30. The method of claim 29 in which a singletransducer of coherent elastic wave energy provides both said first andsaid second sources of coherent radiation.
 31. The method as in claim 29including the step of making a record of said second state ofdistribution of said receiver material in said receiver surface.
 32. Themethod as in claim 31 including the steps of making a reduced sizetransparency of said record and irradiating said transparency withcoherent luminous radiation, whereby an image of said first surface willbe reconstructed.
 33. The method as in claim 29 including the step ofirradiating said second state of distribution of said receiver materialin said receiver surface with coherent luminous radiation, whereby animage of said first surface will be reconstructed.
 34. The method as inclaim 29 in which said step of placing said receiver material comprisesplacing said material in at least two spaced patches in said receiversurface.